In wireless communication apparatuses such as mobile communications, sampling filter apparatuses have been employed, which temporally discretize signals, and perform frequency conversion and filtering operations. As known sampling filter apparatuses, for instance, such a sampling filter apparatus has been disclosed in a patent publication 1. FIG. 8 shows the known sampling filter apparatus described in the patent publication 1.
In FIG. 8, the known sampling filter apparatus includes a switch 2A, a switch 2B, an integrator 3, a weighting and sampling (W & S) element 6, and a control signal generator 7. In response to a clock, an inverted clock, a W&S signal, and a reset signal, which are generated from a control signal generator 7, three processes (namely, resetting, sampling, and holding processes) are carried out.
The filter characteristic of this sampling filter apparatus is determined based upon a weight function. Also, the weight functions depend upon combinations between the W&S element 6 and the W&S signals, while the W&S signals correspond, for instance, to three weight functions (constant, linear, and Gaussian). A signal current which passes through the W&S element 6 is zero outside a sampling window, and is weighted in accordance with the weight functions (constant, linear, and Gaussian) within the sampling window. As previously explained, the outputs of the W&S element 6 are weighted based upon the W&S signals, so that the filter characteristic can be changed.    Patent Publication 1: JP-T-2003-510933 (page 31, FIG. 2A)